Detecting the completion of programming for non-volatile storage

ABSTRACT

A set of non-volatile storage elements are subjected to a programming process in order to store data. During the programming process, one or more verification operations are performed to determine whether the non-volatile storage elements have reached their target condition to store the appropriate data. Programming can be stopped when all non-volatile storage elements have reached their target level or when the number of non-volatile storage elements that have not reached their target level is less than a number or memory cells that can be corrected using an error correction process during a read operation (or other operation). The number of non-volatile storage elements that have not reached their target level can be estimated by counting the number of non-volatile storage elements that have not reached a condition that is different (e.g., lower) than the target level.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to technology for non-volatile storage.

2. Description of the Related Art

Semiconductor memory devices have become more popular for use in variouselectronic devices. For example, non-volatile semiconductor memory isused in cellular telephones, digital cameras, personal digitalassistants, mobile computing devices, non-mobile computing devices andother devices. Electrical Erasable Programmable Read Only Memory(EEPROM) and flash memory are among the most popular non-volatilesemiconductor memories.

Both EEPROM and flash memory utilize a floating gate that is positionedabove and insulated from a channel region in a semiconductor substrate.The floating gate is positioned between source and drain regions. Acontrol gate is provided over and insulated from the floating gate. Thethreshold voltage of the transistor is controlled by the amount ofcharge that is retained on the floating gate. That is, the minimumamount of voltage that must be applied to the control gate before thetransistor is turned on to permit conduction between its source anddrain is controlled by the level of charge on the floating gate.

When programming an EEPROM or flash memory device, typically a programvoltage is applied to the control gate and the bit line is grounded.Electrons from the channel are injected into the floating gate. Whenelectrons accumulate in the floating gate, the floating gate becomesnegatively charged and the threshold voltage of the memory cell israised so that the memory cell is in the programmed state. Moreinformation about programming can be found in U.S. Pat. No. 6,859,397,titled “Source Side Self Boosting Technique For Non-Volatile Memory;”and U.S. Pat. No. 6,917,542, titled “Detecting Over Programmed Memory,”both patents are incorporated herein by reference in their entirety.

Some EEPROM and flash memory devices have a floating gate that is usedto store two ranges of charges and, therefore, the memory cell can beprogrammed/erased between two states, an erased state and a programmedstate that correspond to data “1” and data “0.” Such a device isreferred to as a binary or two-state device.

A multi-state flash memory cell is implemented by identifying multiple,distinct allowed threshold voltage ranges. Each distinct thresholdvoltage range corresponds to a predetermined value for the set of databits. The specific relationship between the data programmed into thememory cell and the threshold voltage ranges of the cell depends uponthe data encoding scheme adopted for the memory cells. For example, U.S.Pat. No. 6,222,762 and U.S. Patent Application Publication No.2004/0255090, both of which are incorporated herein by reference intheir entirety, describe various data encoding schemes for multi-stateflash memory cells.

In some embodiments, the program voltage applied to the control gateincludes a series of pulses that are increased in magnitude with eachsuccessive pulse by a predetermined step size (e.g. 0.2v, 0.3v, 0.4v, orothers). Between pulses, the memory system will verify whether theindividual memory cells have reached their respective target thresholdvoltage ranges. Those memory cells that have reached their targetthreshold voltage range will be locked out of future programming (e.g.,by raising the bit line voltage to Vdd). When all memory cells havereached their target threshold voltage range, programming is complete.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a NAND string.

FIG. 2 is an equivalent circuit diagram of the NAND string.

FIG. 3 is a block diagram of a non-volatile memory system.

FIG. 4 is a block diagram depicting one embodiment of a sense block.

FIG. 5A is a block diagram depicting one embodiment of a memory array.

FIG. 5B depicts a page of data.

FIG. 6 depicts an example set of threshold voltage distributions anddescribes a process for programming non-volatile memory.

FIG. 7 depicts an example set of threshold voltage distributions anddescribes a process for programming non-volatile memory.

FIGS. 8A-C show various threshold voltage distributions and describe aprocess for programming non-volatile memory.

FIG. 9 is a table depicting the order of programming non-volatile memoryin one embodiment.

FIG. 10 depicts an example set of threshold voltage distributions anddescribes a process for programming non-volatile memory.

FIGS. 11A-I show various threshold voltage distributions and describe aprocess for programming non-volatile memory.

FIG. 12 is a flow chart describing one embodiment of a process foroperating non-volatile memory.

FIG. 13 is a flow chart describing one embodiment of a process forprogramming non-volatile memory.

FIGS. 14-17 depicts a control gate signal for one embodiment ofnon-volatile memory.

FIG. 18 depicts an example set of threshold voltage distributions.

FIG. 19 depicts one example threshold voltage distribution.

FIGS. 20-23 depicts a control gate signal for one embodiment ofnon-volatile memory.

FIG. 24 is a flow chart describing one embodiment of a process forprogramming non-volatile memory.

FIG. 25 is a flow chart describing one embodiment of a process forprogramming non-volatile memory.

FIGS. 26A, B and C depict a one embodiment of a programming process thatis performed as part of coarse/fine programming.

FIGS. 27A, B and C depict a one embodiment of a programming process thatis performed as part of coarse/fine programming.

DETAILED DESCRIPTION

In a non-volatile storage system, a set non-volatile storage elementsare subjected to a programming process in order to store a set of data.Programming can be stopped when all non-volatile storage elements havereached their target level or when the number of non-volatile storageelements that have not reached their target level is less than a numberof memory cells that can be corrected using an error correction processduring a read operation (or other operation). The number of non-volatilestorage elements that have not reached their target level can beestimated by counting the number of non-volatile storage elements thathave not reached a condition that is different than the target level.

One example of a non-volatile storage system is a flash memory systemthat uses the NAND structure, which includes arranging multipletransistors in series, sandwiched between two select gates. Thetransistors in series and the select gates are referred to as a NANDstring. FIG. 1 is a top view showing one NAND string. FIG. 2 is anequivalent circuit thereof. The NAND string depicted in FIGS. 1 and 2includes four transistors 100, 102, 104 and 106 in series and sandwichedbetween (drain side) select gate 120 and (source side) select gate 122.Select gate 120 connects the NAND string to a bit line via bit linecontact 126. Select gate 122 connects the NAND string to source line128. Select gate 120 is controlled by applying the appropriate voltagesto select line SGD. Select gate 122 is controlled by applying theappropriate voltages to select line SGS. Each of the transistors 100,102, 104 and 106 has a control gate and a floating gate. For example,transistor 100 has control gate 100CG and floating gate 100FG.Transistor 102 includes control gate 102CG and a floating gate 102FG.Transistor 104 includes control gate 104CG and floating gate 104FG.Transistor 106 includes a control gate 106CG and a floating gate 106FG.Control gate 100CG is connected to word line WL3, control gate 102CG isconnected to word line WL2, control gate 104CG is connected to word lineWL1, and control gate 106CG is connected to word line WL0.

Note that although FIGS. 1 and 2 show four memory cells in the NANDstring, the use of four memory cells is only provided as an example. ANAND string can have less than four memory cells or more than fourmemory cells. For example, some NAND strings will include eight memorycells, 16 memory cells, 32 memory cells, 64 memory cells, 128 memorycells, etc. The discussion herein is not limited to any particularnumber of memory cells in a NAND string. One embodiment uses NANDstrings with 66 memory cells, where 64 memory cells are used to storedata and two of the memory cells are referred to as dummy memory cellsbecause they do not store data.

A typical architecture for a flash memory system using a NAND structurewill include several NAND strings. Each NAND string is connected to thecommon source line by its source select gate controlled by select lineSGS and connected to its associated bit line by its drain select gatecontrolled by select line SGD. Each bit line and the respective NANDstring(s) that are connected to that bit line via a bit line contactcomprise the columns of the array of memory cells. Bit lines are sharedwith multiple NAND strings. Typically, the bit line runs on top of theNAND strings in a direction perpendicular to the word lines and isconnected to a sense amplifier.

Relevant examples of NAND type flash memories and their operation areprovided in the following U.S. Patents/Patent Applications, all of whichare incorporated herein by reference in their entirety: U.S. Pat. No.5,570,315; U.S. Pat. No. 5,774,397; U.S. Pat. No. 6,046,935; U.S. Pat.No. 6,456,528; and U.S. Pat. Publication No. US2003/0002348.

Other types of non-volatile storage devices, in addition to NAND flashmemory, can also be used. For example, a TANOS structure (consisting ofa stacked layer of TaN—Al₂O₃—SiN—SiO₂ on a silicon substrate), which isbasically a memory cell using trapping of charge in a nitride layer(instead of a floating gate), can also be used with the technologydescribed herein. Another type of memory cell useful in flash EEPROMsystems utilizes a non-conductive dielectric material in place of aconductive floating gate to store charge in a non-volatile manner. Sucha cell is described in an article by Chan et al., “A TrueSingle-Transistor Oxide-Nitride-Oxide EEPROM Device,” IEEE ElectronDevice Letters, Vol. EDL-8, No. 3, March 1987, pp. 93-95. A triple layerdielectric formed of silicon oxide, silicon nitride and silicon oxide(“ONO”) is sandwiched between a conductive control gate and a surface ofa semi-conductive substrate above the memory cell channel. The cell isprogrammed by injecting electrons from the cell channel into thenitride, where they are trapped and stored in a limited region. Thisstored charge then changes the threshold voltage of a portion of thechannel of the cell in a manner that is detectable. The cell is erasedby injecting hot holes into the nitride. See also Nozaki et al., “A 1-MbEEPROM with MONOS Memory Cell for Semiconductor Disk Application,” IEEEJournal of Solid-State Circuits, Vol. 26, No. 4, April 1991, pp.491-501, which describes a similar cell in a split-gate configurationwhere a doped polysilicon gate extends over a portion of the memory cellchannel to form a separate select transistor.

Another example is described by Eitan et al., “NROM: A Novel LocalizedTrapping, 2-Bit Nonvolatile Memory Cell,” IEEE Electron Device Letters,vol. 21, no. 11, November 2000, pp. 543-545. An ONO dielectric layerextends across the channel between source and drain diffusions. Thecharge for one data bit is localized in the dielectric layer adjacent tothe drain, and the charge for the other data bit is localized in thedielectric layer adjacent to the source. U.S. Pat. Nos. 5,768,192 and6,011,725 disclose a non-volatile memory cell having a trappingdielectric sandwiched between two silicon dioxide layers. Multi-statedata storage is implemented by separately reading the binary states ofthe spatially separated charge storage regions within the dielectric.Other types of memory devices can also be used.

FIG. 3 illustrates a memory device 210 having read/write circuits forreading and programming a page of memory cells (e.g., NAND multi-stateflash memory) in parallel. Memory device 210 may include one or morememory die or chips 212. Memory die 212 includes an array(two-dimensional or three dimensional) of memory cells 200, controlcircuitry 220, and read/write circuits 230A and 230B. In one embodiment,access to the memory array 200 by the various peripheral circuits isimplemented in a symmetric fashion, on opposite sides of the array, sothat the densities of access lines and circuitry on each side arereduced by half. The read/write circuits 230A and 230B include multiplesense blocks 300 which allow a page of memory cells to be read orprogrammed in parallel. The memory array 200 is addressable by wordlines via row decoders 240A and 240B and by bit lines via columndecoders 242A and 242B. In a typical embodiment, a controller 244 isincluded in the same memory device 210 (e.g., a removable storage cardor package) as the one or more memory die 212. Commands and data aretransferred between the host and controller 244 via lines 232 andbetween the controller and the one or more memory die 212 via lines 234.

Control circuitry 220 cooperates with the read/write circuits 230A and230B to perform memory operations on the memory array 200. The controlcircuitry 220 includes a state machine 222, an on-chip address decoder224 and a power control module 226. The state machine 222 provideschip-level control of memory operations. The on-chip address decoder 224provides an address interface between that used by the host or a memorycontroller to the hardware address used by the decoders 240A, 240B,242A, and 242B. The power control module 226 controls the power andvoltages supplied to the word lines and bit lines during memoryoperations. In one embodiment, power control module 226 includes one ormore charge pumps that can create voltages larger than the supplyvoltage. Control circuitry 220, the decoders 240 A/B & 242A/B, theread/write circuits 230A/B and the controller 244, collectively orseparately, can be referred to as one or more managing circuits.

FIG. 4 is a block diagram of an individual sense block 300 partitionedinto a core portion, referred to as a sense module 480, and a commonportion 490. In one embodiment, there will be a separate sense module480 for each bit line and one common portion 490 for a set of multiplesense modules 480. In one example, a sense block will include one commonportion 490 and eight sense modules 480. Each of the sense modules in agroup will communicate with the associated common portion via a data bus472. For further details, refer to U.S. Patent Application Publication2006/0140007, which is incorporated herein by reference in its entirety.

Sense module 480 comprises sense circuitry 470 that determines whether aconduction current in a connected bit line is above or below apredetermined threshold level. In some embodiments, sense module 480includes a circuit commonly referred to as a sense amplifier. Sensemodule 480 also includes a bit line latch 482 that is used to set avoltage condition on the connected bit line. For example, apredetermined state latched in bit line latch 482 will result in theconnected bit line being pulled to a state designating program inhibit(e.g., Vdd).

Common portion 490 comprises a processor 492, a set of data latches 494and an I/O Interface 496 coupled between the set of data latches 494 anddata bus 420. Processor 492 performs computations. For example, one ofits functions is to determine the data stored in the sensed memory celland store the determined data in the set of data latches. The set ofdata latches 494 is used to store data bits determined by processor 492during a read operation. It is also used to store data bits importedfrom the data bus 420 during a program operation. The imported data bitsrepresent write data meant to be programmed into the memory. I/Ointerface 496 provides an interface between data latches 494 and thedata bus 420.

During read or sensing, the operation of the system is under the controlof state machine 222 that controls the supply of different control gatevoltages to the addressed cell. As it steps through the variouspredefined control gate voltages (the read reference voltages or theverify reference voltages) corresponding to the various memory statessupported by the memory, the sense module 480 may trip at one of thesevoltages and an output will be provided from sense module 480 toprocessor 492 via bus 472. At that point, processor 492 determines theresultant memory state by consideration of the tripping event(s) of thesense module and the information about the applied control gate voltagefrom the state machine via input lines 493. It then computes a binaryencoding for the memory state and stores the resultant data bits intodata latches 494. In another embodiment of the core portion, bit linelatch 482 serves double duty, both as a latch for latching the output ofthe sense module 480 and also as a bit line latch as described above.

It is anticipated that some implementations will include multipleprocessors 492. In one embodiment, each processor 492 will include anoutput line (not depicted in FIG. 4) such that each of the output linesis wired-OR'd together. In some embodiments, the output lines areinverted prior to being connected to the wired-OR line. Thisconfiguration enables a quick determination during the programverification process of when the programming process has completedbecause the state machine receiving the wired-OR line can determine whenall bits being programmed have reached the desired level. For example,when each bit has reached its desired level, a logic zero for that bitwill be sent to the wired-OR line (or a data one is inverted). When allbits output a data 0 (or a data one inverted), then the state machineknows to terminate the programming process. In embodiments where eachprocessor communicates with eight sense modules, the state machine may(in come embodiments) need to read the wired-OR line eight times, orlogic is added to processor 492 to accumulate the results of theassociated bit lines such that the state machine need only read thewired-OR line one time. In some embodiments that have many sensemodules, the wired-OR lines of the many sense modules can be grouped insets of N sense modules, and the groups can then be grouped to form abinary tree.

During program or verify, the data to be programmed is stored in the setof data latches 494 from the data bus 420. The program operation, underthe control of the state machine, comprises a series of programmingvoltage pulses (with increasing magnitudes) concurrently applied to thecontrol gates of the addressed memory cells to that the memory cells areprogrammed at the same time. Each programming pulse is followed by averify process to determine if the memory cell has been programmed tothe desired state. Processor 492 monitors the verified memory staterelative to the desired memory state. When the two are in agreement,processor 492 sets the bit line latch 482 so as to cause the bit line tobe pulled to a state designating program inhibit. This inhibits thememory cell coupled to the bit line from further programming even if itis subjected to programming pulses on its control gate. In otherembodiments the processor initially loads the bit line latch 482 and thesense circuitry sets it to an inhibit value during the verify process.

Data latch stack 494 contains a stack of data latches corresponding tothe sense module. In one embodiment, there are three (or four or anothernumber) data latches per sense module 480. In some implementations (butnot required), the data latches are implemented as a shift register sothat the parallel data stored therein is converted to serial data fordata bus 420, and vice versa. In one preferred embodiment, all the datalatches corresponding to the read/write block of m memory cells can belinked together to form a block shift register so that a block of datacan be input or output by serial transfer. In particular, the bank ofread/write modules is adapted so that each of its set of data latcheswill shift data in to or out of the data bus in sequence as if they arepart of a shift register for the entire read/write block.

Additional information about the structure and/or operations of variousembodiments of non-volatile storage devices can be found in (1) UnitedStates Patent Application Pub. No. 2004/0057287, “Non-Volatile MemoryAnd Method With Reduced Source Line Bias Errors,” published on Mar. 25,2004; (2) United States Patent Application Pub No. 2004/0109357,“Non-Volatile Memory And Method with Improved Sensing,” published onJun. 10, 2004; (3) U.S. Patent Application Pub. No. 20050169082; (4)U.S. Patent Application Pub. 2006/0221692, titled “Compensating forCoupling During Read Operations of Non-Volatile Memory,” Inventor JianChen, filed on Apr. 5, 2005; and (5) U.S. Patent Application Pub.2006/0158947, titled “Reference Sense Amplifier For Non-VolatileMemory,” Inventors Siu Lung Chan and Raul-Adrian Cemea, filed on Dec.28, 2005. All five of the immediately above-listed patent documents areincorporated herein by reference in their entirety.

FIG. 5A depicts an exemplary structure of memory cell array 200. In oneembodiment, the array of memory cells is divided into a large number ofblocks of memory cells. As is common for flash EEPROM systems, the blockis the unit of erase. That is, each block contains the minimum number ofmemory cells that are erased together.

As one example, a NAND flash EEPROM is depicted in FIG. 5A that ispartitioned into 1,024 blocks. However, more or less than 1024 blockscan be used. In each block, in this example, there are 69,624 columnscorresponding to bit lines BL0, BL1, . . . BL69,623. In one embodiment,all the bit lines of a block can be simultaneously selected during readand program operations. Memory cells along a common word line andconnected to any bit line can be programmed (or read) at the same time.In another embodiment, the bit lines are divided into even bit lines andodd bit lines. In an odd/even bit line architecture, memory cells alonga common word line and connected to the odd bit lines are programmed atone time, while memory cells along a common word line and connected toeven bit lines are programmed at another time.

FIG. 5A shows four memory cells connected in series to form a NANDstring. Although four cells are shown to be included in each NANDstring, more or less than four can be used (e.g., 16, 32, 64, 128 oranother number or memory cells can be on a NAND string). One terminal ofthe NAND string is connected to a corresponding bit line via a drainselect gate (connected to select gate drain line SGD), and anotherterminal is connected to the source line via a source select gate(connected to select gate source line SGS).

Each block is typically divided into a number of pages. A page is a unitof programming. One or more pages of data are typically stored in onerow of memory cells. A page can store one or more sectors. A sectorincludes user data and overhead data. Overhead data typically includesan Error Correction Code (ECC) that has been calculated from the userdata of the sector. The controller calculates the ECC when data is beingprogrammed into the array, and also checks it when data is being readfrom the array. In some embodiments, the state machine or othercomponent can calculate and check the ECC. In some alternatives, theECCs and/or other overhead data are stored in different pages, or evendifferent blocks, than the user data to which they pertain. A sector ofuser data is typically 512 bytes, corresponding to the size of a sectorin magnetic disk drives. A large number of pages form a block, anywherefrom 8 pages, for example, up to 32, 64, 128 or more pages. FIG. 5Bdepicts data for a page. Depending on the size of the page, the pagecontains many sectors. Each sector includes user data, error correctioncodes (ECC), and header information.

In some memory systems utilizing multi-state memory cells, each bit ofdata in a memory cell is in a different page. For example, if an arrayof memory cells store three bits of data (eight states or levels ofdata) per memory cell, each memory cell stores data in three pages witheach of the three bits being on a different page. Thus, within a blockin this example, each word line is associated with three pages or aninteger multiple of three pages. Other arrangements are also possible.

The use of error correction coding (ECC) in mass data storage devicesand storage systems, as well as in data communications systems, is wellknown. As fundamental in this art, error correction coding involves thestorage or communication of additional bits (commonly referred to asparity bits, code bits, checksum digits, ECC bits, etc.) that aredetermined or calculated from the “payload” (or original data) data bitsbeing encoded. For example, the storage of error correction coded datain a memory resource involves the encoding of one or more code words toinclude the actual data and the additional code bits, using a selectedcode. Retrieval of the stored data involves the decoding of the storedcode words according to the same code as used to encode the stored codewords. Because the code bits “over-specify” the actual data portion ofthe code words, some number of error bits can be tolerated, without anyloss of actual data evident after decoding.

Many ECC coding schemes are well known in the art. These conventionalerror correction codes are especially useful in large scale memories,including flash (and other non-volatile) memories, because of thesubstantial impact on manufacturing yield and device reliability thatsuch coding schemes can provide, allowing devices that have a fewnon-programmable or defective cells to be useable. Of course, a tradeoffexists between the yield savings and the cost of providing additionalmemory cells to store the code bits (i.e., the code “rate”). Some ECCcodes for flash memory devices tend to have higher code rates (i.e., alower ratio of code bits to data bits) than the codes used in datacommunications applications (which may have code rates as low as ½).

Some memory cells are slower to program or erase than others because ofmanufacturing variations among those cells, because those cells werepreviously erased to a lower threshold voltage than others, because ofuneven wear among the cells within a page, or other reasons. And, ofcourse, some cells cannot be programmed or erased whatsoever, because ofa defect or other reason. As mentioned above, error correction codingprovides the capability of tolerating some number of slow or failedcells, while still maintaining the memory as usable. In someapplications, a page of data is programmed by repeatedly applyingprogramming pulses until all memory cells on that page verify to thedesired programmed state. In these applications, programming terminatesif a maximum number of programming pulses is reached prior to successfulverifying of the programmed page, following which the number of cellsthat have not yet been verified to the desired state is compared with athreshold value, which depends on the capability of the error correctioncoding that will be used in the reading of data from that page. In otherapplications in which the error correction is sufficiently robust,programming and erasing time is saved by terminating the sequence ofprogramming or erasing pulses when the number of slow (or error) cellsthat are not yet fully programmed or erased is fewer than the number ofbits that are correctable.

Error correction is typically performed on a sector-by-sector basis.Thus, each sector will have its own set of ECC codes. This errorcorrection is convenient and useful because, in one embodiment, thesector is the desired unit of data transfer to and from the host system.

At the end of a successful programming process (with verification), thethreshold voltages of the memory cells should be within one or moredistributions of threshold voltages for programmed memory cells orwithin a distribution of threshold voltages for erased memory cells, asappropriate. FIG. 6 illustrates example threshold voltage distributionsfor the memory cell array when each memory cell stores two bits of data.Other embodiments, however, may use more or less than two bits of dataper memory cell (e.g., such as three bits of data per memory cell). FIG.6 shows a first threshold voltage distribution E for erased memorycells. Three threshold voltage distributions, A, B and C for programmedmemory cells are also depicted. In one embodiment, the thresholdvoltages in the distribution E are negative and the threshold voltagesin the A, B and C distributions are positive. As can be seen, thresholdvoltage distribution A is the lowest of A, B and C. Threshold voltagedistribution C is the highest of A, B and C.

Each distinct threshold voltage range of FIG. 6 corresponds topredetermined values for the set of data bits. The specific relationshipbetween the data programmed into the memory cell and the thresholdvoltage levels of the cell depends upon the data encoding scheme adoptedfor the cells. For example, U.S. Pat. No. 6,222,762 and U.S. PatentApplication Publication No. 2004/0255090, “Tracking Cells For A MemorySystem,” filed on Jun. 13, 2003, both of which are incorporated hereinby reference in their entirety, describe various data encoding schemesfor multi-state flash memory cells. In one embodiment, data values areassigned to the threshold voltage ranges using a Gray code assignment sothat if the threshold voltage of a floating gate erroneously shifts toits neighboring threshold voltage distribution, only one bit will beaffected. One example assigns “11” to threshold voltage range E (stateE), “10” to threshold voltage range A (state A), “00” to thresholdvoltage range B (state B) and “01” to threshold voltage range C (stateC). However, in other embodiments, Gray code is not used. Although FIG.6 shows four states, the present invention can also be used with othermulti-state structures including those that include more or less thanfour states.

FIG. 6 shows three read reference voltages, Vra, Vrb and Vrc, forreading data from memory cells. By testing whether the threshold voltageof a given memory cell is above or below Vra, Vrb and Vrc, the systemcan determine what state the memory cell is in. That is, by knowingwhether a memory cell turns on in response to Vra, Vrb and Vrc, theprocessor can figure out which state the memory cell is in. For example,when reading a memory cell, if the memory cell turns on in response toreceiving Vrc but does not turn on in response to Vrb, then the memorycell is in state B.

FIG. 6 also shows three verify reference voltages Vva, Vvb and Vvc. Whenprogramming memory cells to state A, the system will test whether thosememory cells have a threshold voltage greater than or equal to Vva. Whenprogramming memory cells to state B, the system will test whether thememory cells have threshold voltages greater than or equal to Vvb. Whenprogramming memory cells to state C, the system will determine whethermemory cells have their threshold voltage greater than or equal to Vvc.

In general, during verify operations and read operations, the selectedword line is connected to a voltage, a level of which is specified foreach read operation (e.g., see read compare levels Vra, Vrb, and Vrc, ofFIG. 6) or verify operation (e.g. see verify levels Vva, Vvb, and Vvc ofFIG. 6) in order to determine whether a threshold voltage of theconcerned memory cell has reached such level. After applying the wordline voltage, the conduction current of the memory cell is measured todetermine whether the memory cell turned on in response to the voltageapplied to the word line. If the conduction current is measured to begreater than a certain value, then it is assumed that the memory cellturned on and the voltage applied to the word line is greater than thethreshold voltage of the memory cell. If the conduction current is notmeasured to be greater than the certain value, then it is assumed thatthe memory cell did not turn on and the voltage applied to the word lineis not greater than the threshold voltage of the memory cell.

There are many ways to measure the conduction current of a memory cellduring a read or verify operation. In one example, the conductioncurrent of a memory cell is measured by the rate it discharges orcharges a dedicated capacitor in the sense amplifier. In anotherexample, the conduction current of the selected memory cell allows (orfails to allow) the NAND string that includes the memory cell todischarge a corresponding bit line. The voltage on the bit line ismeasured after a period of time to see whether it has been discharged ornot. Note that the technology described herein can be used withdifferent methods known in the art for verifying/reading. Moreinformation about verifying/reading can be found in the following patentdocuments that are incorporated herein by reference in their entirety:(1) United States Patent Application Pub. No. 2004/0057287; (2) UnitedStates Patent Application Pub No. 2004/0109357; (3) U.S. PatentApplication Pub. No. 2005/0169082; and (4) U.S. Patent Application Pub.No. 2006/0221692. The read and verify operations described above areperformed according to techniques known in the art. Thus, many of thedetails explained can be varied by one skilled in the art. Other readand verify techniques known in the art can also be used.

In one embodiment, known as full sequence programming, memory cells canbe programmed from the erased state E directly to any of the programmedstates A, B or C. For example, a population of memory cells to beprogrammed may first be erased so that all memory cells in thepopulation are in erased state E. While a first set of memory cells isbeing programmed from state E to state A, a second set of memory cellsis being programmed from state E to state B and a third set of memorycells is being programmed from state E to state C. Full sequenceprogramming is graphically depicted by the three curved arrows of FIG.6.

FIG. 7 illustrates an example of a two-pass technique of programming amulti-state memory cell that stores data for two different pages: alower page and an upper page. Four states (threshold voltagedistributions) are depicted: state E (11), state A (10), state B (00)and state C (01). For state E, both pages store a “1.” For state A, thelower page stores a “0” and the upper page stores a “1.” For state B,both pages store “0.” For state C, the lower page stores “1” and theupper page stores “0.” Note that although specific bit patterns havebeen assigned to each of the states, different bit patterns may also beassigned.

In a first programming pass, the memory cell's threshold voltage levelis set according to the data bit to be programmed into the lower logicalpage. If that data bit is a logic “1,” the threshold voltage is notchanged since it is in the appropriate state as a result of having beenearlier erased. However, if the data bit to be programmed is a logic“0,” the threshold level of the cell is increased to be state A, asshown by arrow 530.

In a second programming pass, the memory cell's threshold voltage levelis set according to the data bit being programmed into the upper logicalpage. If the upper logical page bit is to store a logic “1,” then noprogramming occurs since the cell is in one of the states E or A,depending upon the programming of the lower page bit, both of whichcarry an upper page bit of “1.” If the upper page data bit is to be alogic “0,” then the threshold voltage is shifted. If the first passresulted in the memory cell remaining in the erased state E, then in thesecond phase the memory cell is programmed so that the threshold voltageis increased to be within state C, as depicted by arrow 534. If thememory cell had been programmed into state A as a result of the firstprogramming pass, then the memory cell is further programmed in thesecond pass so that the threshold voltage is increased to be withinstate B, as depicted by arrow 532. The result of the second pass is toprogram the cell into the state designated to store a logic “0” for theupper page without changing the data for the lower page.

In one embodiment, a system can be set up to perform full sequencewriting if enough data is written to fill up a word line. If not enoughdata is being written, then the programming process can program thelower page with the data received. When subsequent data is received, thesystem will then program the upper page. In yet another embodiment, thesystem can start writing in the mode that programs the lower page andconvert to full sequence programming mode if enough data is subsequentlyreceived to fill up an entire (or most of a) word line's memory cells.More details of such an embodiment are disclosed in U.S. PatentApplication titled “Pipelined Programming of Non-Volatile Memories UsingEarly Data,” Pub. No. 2006/0126390, Ser. No. 11/013,125, filed on Dec.14, 2004, inventors Sergy Anatolievich Gorobets and Yan Li, incorporatedherein by reference in its entirety.

FIGS. 8A-C disclose another process for programming non-volatile memorythat reduces the effect of floating gate to floating gate coupling. Inone example of an implementation of the process taught by FIGS. 8A-C,the non-volatile memory cells store two bits of data per memory cell,using four data states. For example, assume that state E is the erasedstate and states A, B and C are the programmed states. State E storesdata 11. State A stores data 01. State B stores data 10. State C storesdata 00. This is an example of non-Gray coding because both bits changebetween adjacent states A & B. Other encodings of data to physical datastates can also be used. Each memory cell stores two data in two pages.For reference purposes these pages of data will be called upper page andlower page; however, they can be given other labels. With reference tostate A for the process of FIGS. 8A-C, the upper page stores bit 0 andthe lower page stores bit 1. With reference to state B, the upper pagestores bit 1 and the lower page stores bit 0. With reference to state C,both pages store bit data 0.

The programming process of FIGS. 8A-C is a two-step process. In thefirst step, the lower page is programmed. If the lower page is to remaindata 1, then the memory cell state remains at state E. If the data is tobe programmed to 0, then the threshold of voltage of the memory cell israised such that the memory cell is programmed to state B′. FIG. 8Atherefore shows the programming of memory cells from state E to stateB′. State B′ depicted in FIG. 8A is an interim state B; therefore, theverify point is depicted as Vvb′, which is lower than Vvb.

In one embodiment, after a memory cell (on word line WLn is programmedfrom state E to state B′, its neighbor memory cell (on word line WLn+1)on the NAND string will then be programmed with respect to its lowerpage. For example, after the lower page for a memory cell connected toWL0 is programmed, the lower page for a memory cell (the neighbor memorycell) on the same NAND string but connected to WL1 can be programmed.After programming the neighbor memory cell, the floating gate tofloating gate coupling effect will raise the apparent threshold voltageof earlier memory cell to be programmed if that earlier memory cell hada threshold voltage raised from state E to state B′. This will have theeffect of widening the threshold voltage distribution for state B′, asdepicted by threshold voltage distribution 550 in FIG. 8B. This apparentwidening of the threshold voltage distribution will be remedied whenprogramming the upper page.

FIG. 8C depicts the process of programming the upper page. If the memorycell is in erased state E and the upper page is to remain at 1, then thememory cell will remain in state E. If the memory cell is in state E andits upper page data is to be programmed to 0, then the threshold voltageof the memory cell will be raised so that the memory cell is in state A.If the memory cell was in intermediate threshold voltage distribution550 and the upper page data is to remain at 1, then the memory cell willbe programmed to final state B. If the memory cell is in intermediatethreshold voltage distribution 550 and the upper page data is to becomedata 0, then the threshold voltage of the memory cell will be raised sothat the memory cell is in state C. The process depicted by FIGS. 8A-Creduces the effect of coupling between floating gates because only theupper page programming of neighbor memory cells will have an effect onthe apparent threshold voltage of a given memory cell.

Although FIGS. 8A-C provide an example with respect to four data statesand two pages of data, the concepts taught by FIGS. 8A-C can be appliedto other implementations with more or less than four states, differentthan two pages, and/or other data encodings.

FIG. 9 is a table that describes one embodiment of the order forprogramming memory cells utilizing the programming method of FIGS. 8A-C.For memory cells connected to word line WL0, the lower page forms page 0and the upper page forms page 2. For memory cells connected to word lineWL1, the lower page forms page 1 and the upper page forms page 4. Formemory cells connected to word line WL2, the lower page forms page 3 andthe upper page forms page 6. For memory cells connected to word lineWL3, the lower page forms page 5 and the upper page forms page 7. Memorycells are programmed according to page number, from page 0 to page 7. Inother embodiments, other orders of programming can also be used.

FIG. 10 illustrates example threshold voltage distributions (also calleddata states) for the memory cell array when each memory cell storesthree bits of multi-state data. Other embodiment, however, may use moreor less than three bits of data per memory cell (e.g., such as four ormore bits of data per memory cell).

In the example of FIG. 10, each memory cell stores three bits of data;therefore, there are eight valid data states S0-S7. In one embodiment,data state S0 is below 0 volts and data states S1-S7 are above 0 volts.In other embodiments, all eight data states are above 0 volts, or otherarrangements can be implemented. In one embodiment, the thresholdvoltage distribution S0 is wider than distributions S1-S7.

In one embodiment, S0 is for erased memory cells. Data is programmedfrom S0 to S1-S7. As can be seen from FIG. 10, of S1-S7, S1 is thelowest in magnitude and S7 is the highest in magnitude (e.g. mostextreme).

Each data state corresponds to a unique value for the three data bitsstored in the memory cell. In one embodiment, S0=111, S1=110, S2=101,S3=100, S4=011, S5=010, S6=001 and S7=000. Other mapping of data tostates S0-S7 can also be used. In one embodiment, all of the bits ofdata stored in a memory cell are stored in the same logical page. Inother embodiments, each bit of data stored in a memory cell correspondsto different logical pages. Thus, a memory cell storing three bits ofdata would include data in a first page, data in a second page and datain a third page. In some embodiments, all of the memory cells connectedto the same word line would store data in the same three pages of data.In some embodiments, the memory cells connected to a word line can begrouped into different sets of pages (e.g., by odd and even bit lines,or by other arrangements).

In some prior art devices, the memory cells will be erased to state S0.From state S0, the memory cells can be programmed to any of statesS1-S7. In one embodiment, known as full sequence programming, memorycells can be programmed from the erased state S0 directly to any of theprogrammed states S1-S7. For example, a population of memory cells to beprogrammed may first be erased so that all memory cells in thepopulation are in erased state S0. While some memory cells are beingprogrammed from state S0 to state S1, other memory cells are beingprogrammed from state S0 to state S2, state S0 to state S3, state S0 tostate S4, state S0 to state S5, state S0 to state S6, and state S0 tostate S7. Full sequence programming is graphically depicted by the sevencurved arrows of FIG. 10

FIG. 10 shows a set of target verify levels Vv1, Vv2, Vv3, Vv4, Vv5,Vv6, and Vv7. These target verify levels are used as comparison levelsduring the programming process. For example, when programming memorycells to state 1, the system will check to see if the threshold voltagesof the memory cells has reached Vv1. If the threshold voltage of amemory cell has not reached Vv1, then programming will continue for thatmemory cell until its threshold voltage is greater than or equal to Vv1.If the threshold voltage of a memory cell has reached Vv1, thenprogramming will stop for that memory cell. Target verify level Vv2 isused for memory cells being programmed to state 2. Target verify levelVv3 is used for memory cells being programmed to state 3. Target verifylevel Vv4 is used for memory cells being programmed to state 4. Targetverify level Vv5 is used for memory cells being programmed to state 5.Target verify level Vv6 is used for memory cells being programmed tostate 6. Target verify level Vv7 is used for memory cells beingprogrammed to state 7.

FIG. 10 also shows a set of read compare levels Vr1, Vr2, Vr3, Vr4, Vr5,Vr6, and Vr7. These read compare levels are used as comparison levelsduring the read process. By testing whether the memory cells turn on orremain off in response to the read compare levels Vr1, Vr2, Vr3, Vr4,Vr5, Vr6, and Vr7 being separately applied to the control gates of thememory cells, the system can determine which states that memory cellsare storing data for.

FIGS. 11A-11I disclose another process for programming multi-state data.Prior to the first step, the memory cells will be erased so that theyare in the erase threshold distribution of state S0. The process ofFIGS. 11A-11I assumes that each memory cell stores three bits of data,with each bit for a given memory cell being in a different page. Thefirst bit of data (the leftmost bit) is associated with the first page.The middle bit is associated with the second page. The rightmost bit isassociated with the third page. In one embodiment, the correlation ofdata states to data is as follows: S0=111, S1=110, S2=101, S3=100,S4=011, S5=010, S6=001 and S7=000. However, other embodiments can useother data encoding schemes.

When programming the first page (as described in FIG. 11A), if the bitis to be data “1” then the memory cell will stay in state S0 (thresholdvoltage distribution 602). If the bit is to be data “0” then the memorycell is programmed to state S4 (threshold voltage distribution 604).After adjacent memory cells are programmed, capacitive coupling betweenadjacent floating gates may cause the state S4 to widen as depicted inFIG. 11B. State S0 may also widen, but there is sufficient marginbetween S0 and S1 to ignore the effect. More information aboutcapacitive coupling between adjacent floating gates can be found in U.S.Pat. No. 5,867,429 and U.S. Pat. No. 6,657,891, both of which areincorporated herein by reference in their entirety.

When programming the second page (see FIG. 11C), if the memory cell isin state S0 and the second page bit is data “1” then the memory cellstays in state S0. In some embodiments, the programming process for thesecond page will tighten threshold voltage distribution 602 to a new S0.If the memory cell was in state S0 and the data to be written to thesecond page is “0,” then the memory cell is moved to state S2 (thresholdvoltage distribution 606). State S2 has a verify point of C*. If thememory cell was in state S4 and the data to be written to the memorycell is “1” then the memory cell remains in S4. However, state S4 istightened by moving the memory cells from threshold voltage distribution604 to threshold voltage distribution 608 for state S4, as depicted inFIG. 11C. Threshold voltage distribution 608 has a verify point of E*(as compared to E** of threshold voltage distribution 604). If thememory cell is in state S4 and the data to be written to the second pageis a “0” then the memory cell has its threshold voltage moved to stateS6 (threshold voltage distribution 610), with a verify point of G*.

After the adjacent memory cells are programmed, states S0, S2, S4 and S6are widened due to the floating gate to floating gate coupling, asdepicted by threshold voltages distributions 602, 606, 608 and 610 ofFIG. 11D.

FIGS. 11E, 11F, 11G and 11H depict the programming of the third page.While one graph can be used, the programming process is depicted in fourgraphs for visibility reasons. After the second page has beenprogrammed, the memory cells are either in states S0, S2, S4 or S6. FIG.11E shows the memory cells that are in state S0 being programmed for thethird page. FIG. 11F shows the memory cells that are in state S2 beingprogrammed for the third page. FIG. 11G shows the memory cells that arein state S4 being programmed for the third page. FIG. 11H shows thememory cells that are in state S6 being programmed for the third page.FIG. 11I shows the threshold voltage distributions after the processesof FIGS. 11E, 11F, 11G and 11H have been performed on the population ofmemory cells (concurrently or serially).

If a memory cell is in state S0 and the third page data is “1” then thememory cell remains at state S0. If the data for the third page is “0”then the threshold voltage for the memory cell is raised to be in stateS1, with a verify point of B (see FIG. 11E).

If a memory cell is in state S2 and the data to be written in the thirdpage is “1,” then the memory cell will remain in state S2 (see FIG.11F). However, some programming will be performed to tighten thethreshold distribution 606 to a new state S2 with a verify point of C.If the data to be written to the third page is “0,” then the memory cellwill be programmed to state S3, with a verify point of D.

If a memory cell is in state S4 and the data to be written to the thirdpage is “1” then the memory cell will remain in state S4 (see FIG. 11G).However, some programming will be performed so that threshold voltagedistribution 608 will be tightened to new state S4 with a verify pointof E. If a memory cell is in state S4 and the data to be written to thethird page is “0” then the memory cell will have its threshold voltageraised to be in state S5, with a verify point of F (see FIG. 11G).

If the memory cell is in state S6 and the data to be written to thethird page is “1” then the memory cell will remain in state S6 (see FIG.11H). However, there will be some programming so that the thresholdvoltage distribution 510 is tightened to be in new state S6, with averify point at G. If the third page data is “0” then the memory cellwill have its threshold voltage programmed to state S7, with a verifypoint at H (see FIG. 11H). At the conclusion of the programming of thethird page, the memory cell will be in one of the eight states depictedin FIG. 11I.

FIG. 12 is a flow chart describing a process for operating memory cellsconnected to a selected word line. In one embodiment, the process ofFIG. 12 is used to program a block of memory cells. In oneimplementation of the process of FIG. 12, memory cells arepre-programmed in order to maintain even wear on the memory cells (step650). In one embodiment, the memory cells are preprogrammed to thehighest state, a random pattern, or any other pattern. In someimplementations, pre-programming need not be performed.

In step 652, memory cells are erased (in blocks or other units) prior toprogramming. Memory cells are erased in one embodiment by raising thep-well to an erase voltage (e.g., 20 volts) for a sufficient period oftime and grounding the word lines of a selected block while the sourceand bit lines are floating. In blocks that are not selected to beerased, word lines are floated. Due to capacitive coupling, theunselected word lines, bit lines, select lines, and the common sourceline are also raised to a significant fraction of the erase voltagethereby impeding erase on blocks that are not selected to be erased. Inblocks that are selected to be erased, a strong electric field isapplied to the tunnel oxide layers of selected memory cells and theselected memory cells are erased as electrons of the floating gates areemitted to the substrate side, typically by Fowler-Nordheim tunnelingmechanism. As electrons are transferred from the floating gate to thep-well region, the threshold voltage of a selected cell is lowered.Erasing can be performed on the entire memory array, on individualblocks, or another unit of cells. In one embodiment, after erasing thememory cells, all of the erased memory cells will be in state E or S0.One implementation of an erase process includes applying several erasepulses to the p-well and verifying between erase pulses whether the NANDstrings are properly erased.

At step 654, soft programming is (optionally) performed to narrow thedistribution of erased threshold voltages for the erased memory cells.Some memory cells may be in a deeper erased state than necessary as aresult of the erase process. Soft programming can apply programmingpulses to move the threshold voltage of the deeper erased memory cellsto the erase threshold distribution (e.g., state E or S0).

In step 656, the memory cells of the block are programmed. Afterprogramming, the memory cells of the block can be read (step 658). Manydifferent read processes known in the art can be used to read data. Insome embodiments, the read process includes using ECC to correct errors.The data read, is output to the hosts that requested the read operation.The ECC process can be performed by the state machine, the controller oranother device.

FIG. 12 shows that the erase-program cycle can happen many times withoutor independent of reading, the read process can occur many times withoutor independent of programming, and the read process can happen any timeafter programming. The process of FIG. 12 can be performed at thedirection of the state machine using the various circuits describedabove. In other embodiments, the process of FIG. 12 can be performed atthe direction of the controller using the various circuits describedabove.

FIG. 13 is a flow chart describing one embodiment of a process forperforming programming on memory cells connected to a common word lineto one or more target conditions (e.g., data states or threshold voltageranges). The process of FIG. 13 can be performed one or multiple timesduring step 656 of FIG. 12. For example, the process of FIG. 13 can beused to program memory cells (e.g., full sequence programming) fromstate E or S0 directly to any of states A-C (see FIG. 6) or S1-S7 (seeFIG. 10). Alternatively, the process of FIG. 13 can be used to performone or each of the phases of the process of FIG. 7, one or each of thesteps of the process of FIGS. 8A-C, or one or each of the steps of theprocess of FIGS. 11A-I. For example, when performing the process of FIG.7, the process of FIG. 13 is used to implement the first phase thatincludes programming some of the memory cells from state E to state A.The process of FIG. 13 can then be used again to implement the secondphase that includes programming some of the memory cells from state E tostate C while programming other memory cells from state A to state B.

Typically, the program voltage applied to the control gate during aprogram operation is applied as a series of program pulses. Betweenprogramming pulses are a set of verify pulses to perform verification.In many implementations, the magnitude of the program pulses isincreased with each successive pulse by a predetermined step size. Instep 670 of FIG. 13, the programming voltage (Vpgm) is initialized tothe starting magnitude (e.g., ˜12-16V or another suitable level) and aprogram counter PC maintained by state machine 222 is initialized at 1.In step 672, a program pulse of the program signal Vpgm is applied tothe selected word line (the word line selected for programming). In oneembodiment, the group of memory cells being programmed are all connectedto the same word line (the selected word line). The unselected wordlines receive one or more boosting voltages (e.g., ˜9 volts) to performboosting schemes known in the art. If a memory cell should beprogrammed, then the corresponding bit line is grounded. On the otherhand, if the memory cell should remain at its current threshold voltage,then the corresponding bit line is connected to Vdd to inhibitprogramming. In step 672, the program pulse is concurrently applied toall memory cells connected to the selected word line so that all of thememory cells connected to the selected word line are programmedconcurrently. That is, they are programmed at the same time (or duringoverlapping times). In this manner all of the memory cells connected tothe selected word line will concurrently have their threshold voltagechange, unless they have been locked out from programming.

In step 674, the states of the selected memory cells are verified usingthe appropriate set of target levels. Step 674 includes performing oneor more verify operations. If it is detected that the threshold voltageof a memory cell has reached the appropriate target level, then thatmemory cell is locked out of further programming by, for example,raising its bit line voltage to Vdd during subsequent programmingpulses.

In step 676, it is checked whether all the memory cells have reachedtheir target threshold voltages. If so, the programming process iscomplete and successful because all selected memory cells wereprogrammed and verified to their target states. A status of “PASS” isreported in step 678. If, in 676, it is determined that not all of thememory cells have reached their target threshold voltages, then theprogramming process continues to step 680.

In step 680, the system counts the number of memory cells that have notyet reached their respective target threshold voltage distribution. Thatis, the system counts the number of cells that have failed the verifyprocess. This counting can be done by the state machine, the controller,or other logic. In one implementation, each of the sense block 300 (seeFIG. 3) will store the status (pass/fail) of their respective cells.These values can be counted using a digital counter. As described above,many of the sense blocks have an output signal that is wire-Or'dtogether. Thus, checking one line can indicate that no cells of a largegroup of cells have failed verify. By appropriately organizing the linesbeing wired-Or together (e.g., a binary tree-like structure), a binarysearch method can be used to determine the number of cells that havefailed. In such a manner, if a small number of cells failed, thecounting is completed rapidly. If a large number of cells failed, thecounting takes a longer time. More information can be found in UnitedStates Patent Publication 2008/0126676, incorporated herein byreference. In another alternative, each of the sense amplifiers canoutput an analog voltage or current if its corresponding cell has failedand an analog voltage or current summing circuit can be used to countthe number of cells that have failed.

In one embodiment, there is one total counted, which reflects the totalnumber of memory cells currently being programmed that have failed thelast verify step. In another embodiment, separate counts are kept foreach data state.

In step 682, it is determined whether the count from step 680 is lessthan or equal to a predetermined limit. In one embodiment, thepredetermined limit is the number of bits that can be corrected by ECCduring a read process for the page of memory cells. If the number offailed cells is less than or equal to the predetermined limit, than theprogramming process can stop and a status of “PASS” is reported in step678. In this situation, enough memory cells programmed correctly suchthat the few remaining memory cells that have not been completelyprogrammed can be corrected using ECC during the read process (see step658 of FIG. 12).

In another embodiment, the predetermined limit can be less than thenumber of bits that can be corrected by ECC during a read process toallow for future errors. When programming less than all of the memorycells for a page, or comparing a count for only one data state (or lessthan all states), than the predetermined limit can be a portion(pro-rata or not pro-rata) of the number of bits that can be correctedby ECC during a read process for the page of memory cells. In someembodiments, the limit is not predetermined. Instead, it changes basedon the number of errors already counted for the page, the number ofprogram-erase cycles performed, temperature or other criteria.

If the number of failed cells is not less than the predetermined limit,than the programming process continues at step 684 and the programcounter PC is checked against the program limit value (PL). One exampleof a program limit value is 20; however, other values can be used. Ifthe program counter PC is not less than the program limit value PL, thenthe program process is considered to have failed and a status of FAIL isreported in step 688. If the program counter PC is less than the programlimit value PL, then the process continues at step 686 during which timethe Program Counter PC is incremented by 1 and the program voltage Vpgmis stepped up to the next magnitude. For example, the next pulse willhave a magnitude greater than the previous pulse by a step size (e.g., astep size of 0.1-0.4 volts). After step 686, the process loops back tostep 672 and another program pulse is applied to the selected word line.

FIG. 14 shows a portion of the voltage waveform applied to the selectedword line and, therefore, to the control gates of the memory cellsconnected to the selected word line during the programming for theprocess of FIG. 13. The waveform shows the programming pulse (Program)applied during step 672, the verify pulses (Verify) applied during step674 and the time period (count failed cells) for counting the failedcells during step 680 for parts of three iterations of the loopscomprising steps 672-686 of FIG. 13. The example of FIG. 14 correspondsto the embodiments with two bits per memory cell and four data states.Therefore, the verify process includes a verify pulse at Vva, a verifypulse at Vvb and a verify pulse a Vvc. In embodiments with three bitsper memory cell and eight data states, there may be up to eight verifypulses. Note that some embodiments will use less than all three or eightverify pulses in some iterations when it is clear that no memory cellneeds to be tested for certain data states. Additionally, embodimentswith different numbers of data states will use different numbers ofverify pulses. In the embodiment of FIG. 14, the verify operations (step674) and the counting the failed cells (step 680) are performed betweenprogramming pulses. Therefore, as soon as it is determined that allmemory cells have verified or that the number of memory cells thatfailed verification is less than the predetermined limit (or a limitthat is not predetermined), than the programming process can stopwithout applying the next programming pulse.

FIG. 15 shows a portion of another embodiment of the voltage waveformapplied to the selected word line and, therefore, to the control gatesof the memory cells connected to the selected word line during theprogramming process of FIG. 13. This waveform shows the programmingpulse (Program) applied during step 672, the verify pulses (Verify)applied during step 674 and the time period (count failed cells) forcounting the failed cells during step 680 for parts of three iterationsof the loops comprising steps 672-686 of FIG. 13. In the embodiment ofFIG. 15, the verify operations (step 674) are performed betweenprogramming pulses. However, the counting of the failed cells isperformed during the next program pulse, which can save time. When it isdetermined that all memory cells have verified or that the number ofmemory cells that failed verification is less than the predeterminedlimit (or a limit that is not predetermined), than the programmingprocess can stop; however, the next programming pulse has already beenapplied. As discussed above, the results of the verification process canbe stored in latches 494. These latches can be read during the nextprogram pulse.

FIG. 16 shows a portion of another embodiment of the voltage waveformapplied to the selected word line and, therefore, to the control gatesof the memory cells connected to the selected word line. This waveformshows the programming pulse (Program) applied during step 672, theverify pulses (Verify) applied during step 674 and the time period(count failed cells) for counting the failed cells during step 680 forparts of three iterations of the loops comprising steps 672-686 of FIG.13. The embodiment of FIG. 16 pertains to a programming process that isonly verifying for one state. For example, when programming data tofour, eight or more states, the process may reach a condition where thememory cells have all reached their target states except for the memorycells being programmed to the highest state (e.g., state C or state S7).At that point, the verify process will only perform a verify at Vvc (seeFIG. 6) or Vv7 (see FIG. 7). Thus, FIG. 16 only shows on verify pulsefor testing whether the memory cells the highest data state (or anotherstate that is not the highest). In another example, the waveform of FIG.16 can be used with a programming operation that is only programming toone state; for example, the first phase of the process of FIG. 7, theprocess of FIG. 8A, the process of FIG. 11A or other processes. Forprogramming operations that program to more than one state, theadditional verify pulses can be added to the waveform, as appropriate.In the embodiment of FIG. 16, the verify operations (step 674) and thecounting the failed cells (step 680) are performed between programmingpulses.

FIG. 17 shows a portion of another embodiment of the voltage waveformapplied to the selected word line and, therefore, to the control gatesof the memory cells connected to the selected word line. This waveformshows the programming pulse (Program) applied during step 672, theverify pulses (Verify) applied during step 674 and the time period(count failed cells) for counting the failed cells during step 680 forparts of three iterations of the loops comprising steps 672-686 of FIG.13. Like FIG. 16, the waveform of FIG. 17 pertains to a programmingprocess that is only verifying for one state. In the embodiment of FIG.17, the verify operations (step 674) are performed between programmingpulses. However, the counting of the failed cells is performed duringthe next program pulse.

Because the program voltage is applied to all memory cells connected toa word line, an unselected memory cell (a memory cell that is not to beprogrammed) on the word line may become inadvertently programmed. Theunintentional programming of the unselected cell on the selected wordline is referred to as “program disturb.” For example, a memory cell instate E may have its threshold voltage increased to a level outside ofstate E. FIG. 18 shows threshold voltage versus number of memory cellsfor data states E, A, B and C for a population of memory cells during aprogramming process. State E is depicted as having a subset of itsmemory cells, indicated by shaded region 702, being subjected to programdisturb so that their respective threshold voltage is above the levelnormally intended to be part of state E. The program disturb is moresevere when programming memory cells to the highest (most extreme) state(e.g. state C or S7). This is because it generally takes more voltagepulses to program memory cells to the highest state and the more pulsesapplied increases the chance of program disturb. Furthermore, since themagnitude of the voltage increases with each pulse, the highest datastate is programmed with higher voltages, which also can increase thechance of program disturb.

FIG. 18 also shows that some of the memory cells (see shaded region 704)that are being programmed to highest state C have not yet reached Vvc.In this case, continuing to program the memory cells represented byshaded region 704 will only exacerbate the program disturb of the memorycells in shaded region 702. Therefore, the programming process describedabove stops the programming of memory cells to the highest state (andother data states) before all memory cells have reached the target(e.g., have reached Vvc) in order to reduce (or prevent furtherexacerbation) of the program disturb. However, the programming is onlystopped when the number of memory cells not fully programmed is lessthan the number of cells that can be corrected by ECC, as explainedabove with respect to steps 680 and 682 of FIG. 13.

In one embodiment, instead of counting the number of cells that arebelow the verify compare value (e.g., Vvc), the system can count thenumber of cells that are below an intermediate compare value and usethat count as an estimate of how many cells are below the verify comparevalue. For example, FIG. 19 shows the threshold voltage distribution fordata state C with verify compare value Vvc and read compare value Vrc.FIG. 19 also shows an intermediate compare value VvcL. In one embodimentof step 680 of FIG. 13, the system will count the number of memory cellssupposed to be programmed to state C that have their threshold voltageless than VvcL in order to estimate the number of memory cells supposedto be programmed to state C that have their threshold voltage less thanVvc.

The number of memory cells that have their threshold voltage less thanVvcL is proportional to the number of memory cells that have theirthreshold voltage less than Vvc. For example, if VvcL is 0.4-0.5v lowerthan Vvc, than the number of memory cells that have their thresholdvoltage less than VvcL is approximately one tenth ( 1/10) of the numberof memory cells that have their threshold voltage less than Vvc. If VvcLis 0.8-1.0v lower than Vvc, than the number of memory cells that havetheir threshold voltage less than VvcL is approximately one hundredth (1/100) of the number of memory cells that have their threshold voltageless than Vvc. In some implementations, the number of cells that arecounted as being below the compare value will reduce with a factor of 10for each 0.4-0.5v. FIG. 19 shows shaded region 712 representing thosememory cells with a threshold voltage below Vvc and above Vrc. Shadedregion 714 represents those memory cells with a threshold voltage belowVrc and above VvcL. Shaded region 714 represents those memory cells witha threshold voltage below VvcL. Thus, the number of memory cells thathave their threshold voltage less than Vvc is the sum of shaded regions712+714+716. As can be seen this is significantly larger than the numberof memory cells that have their threshold voltage less than VvcL. Insome embodiments, counting the number of memory cells below theintermediate compare value VvcL will be faster than counting the numberof memory cells below Vvc.

FIG. 20 shows a portion of the voltage waveform applied to the selectedword line (and, therefore, to the control gates of the memory cellsconnected to the selected word line) during the programming process ofFIG. 13 for the embodiment of step 680 in which the system will countthe number of memory cells supposed to be programmed to state C thathave their threshold voltage less than intermediate compare value VvcL.If the number of memory cells supposed to be programmed to state C thathave their threshold voltage less than VvcL is less than or equal to aparticular limit (see step 682 of FIG. 13), then the programming processis concluded. Since VvcL is lower than Vvc, the particular limitcompared against is lower than if comparing against Vvc. In the twoexamples above, the limit used for VvcL is 10 or 100 times smaller thanthe limit used for Vvc. The waveform of FIG. 20 shows the programmingpulse (Program) applied during step 672, the verify pulses (Verify)applied during step 674 and the time period (count failed cells) forcounting the failed cells during step 680 for parts of three iterationsof the loops comprising steps 672-686 of FIG. 13. In this embodiment,step 680 (count failed cells) includes applying a voltage pulse of VvcLin order to test whether the memory cells have a threshold voltage of atleast VvcL. Other methods of testing the threshold voltage can also beused. Additionally note that although the voltage pulse is depicted as aperfect square wave, in reality the voltage pulse (and the other pulsesdepicted in this figure and other figures) is not likely to be a perfectsquare and in some cases it may be a different shape than a square wave.

The example of FIG. 20 corresponds to the embodiments with two bits permemory cell and four data states. Therefore, the verify process includesa verify pulse at Vva, a verify pulse at Vvb and a verify pulse a Vvc.In embodiments with three bits per memory cell and eight data states,there may be up to eight verify pulses. Note that some embodiments willuse less than all three or eight verify pulses in some iterations whenit is clear that no memory cell needs to be tested for certain datastates. Additionally, embodiments with different numbers of data stateswill use different numbers of verify pulses. In the embodiment of FIG.20, the verify operations (step 674) and the counting the failed cells(step 680) are performed between programming pulses. Therefore, as soonas it is determined that all memory cells have verified or that thenumber of memory cells that failed verification is less than a limit,than the programming process can stop without applying the nextprogramming pulse.

FIG. 21 shows a portion of the voltage waveform applied to the selectedword line (and, therefore, to the control gates of the memory cellsconnected to the selected word line) for another embodiment of step 680of FIG. 13, in which the system will count the number of memory cellssupposed to be programmed to state C that have their threshold voltageless than VvcL. This waveform shows the programming pulse (Program)applied during step 672, the verify pulses (Verify) applied during step674 and the time period (count failed cells) for counting the failedcells during step 680 for parts of three iterations of the loopscomprising steps 672-686 of FIG. 13. In this embodiment, step 680 (countfailed cells) includes applying a voltage pulse of VvcL in order to testwhether the memory cells have a threshold voltage of at least VvcL.Other methods of testing the threshold voltage can also be used. In theembodiment of FIG. 21, the verify operations (step 674) are performedbetween programming pulses. However, the counting of the failed cells(step 680) is performed during the next program pulse. As discussedabove, the results of the verification process can be stored in latches494. These latches can be read during the next program pulse.

FIG. 22 shows a portion of the voltage waveform applied to the selectedword line (and, therefore, to the control gates of the memory cellsconnected to the selected word line) for another embodiment of step 680of FIG. 13, in which the system will count the number of memory cellssupposed to be programmed to state C that have their threshold voltageless than VvcL. This waveform shows the programming pulse (Program)applied during step 672, the verify pulses (Verify) applied during step674 and the time period (count failed cells) for counting the failedcells during step 680 for parts of three iterations of the loopscomprising steps 672-686 of FIG. 13. The embodiment of FIG. 16 pertainsto a programming process that is only verifying for one state. Forexample, when programming data to four, eight or more states, theprocess may reach a condition where the memory cells have all reachedtheir target states except for the memory cells being programmed to thehighest state (e.g., state C or state S7). At that point, the verifyprocess will only perform a verify at Vvc (see FIG. 6) or Vv7 (see FIG.7). Thus, FIG. 22 only shows one verify pulse for testing whether thememory cells reached the highest data state (or another state that isnot the highest). The waveform of FIG. 22 can be used with a programmingoperation that is only programming to one state; for example, the firstphase of the process of FIG. 7, the process of FIG. 8A, the process ofFIG. 11A or other processes. For programming operations that program tomore than one state, the additional verify pulses can be added to thewaveform, as appropriate. In the embodiment of FIG. 22, the verifyoperations (step 674) and the counting the failed cells (step 680) areperformed between programming pulses. In this embodiment, like theembodiment of FIG. 21, step 680 (count failed cells) includes applying avoltage pulse of VvcL in order to test whether the memory cells have athreshold voltage of at least VvcL. Other methods of testing thethreshold voltage can also be used.

FIG. 23 shows a portion of the voltage waveform applied to the selectedword line (and, therefore, to the control gates of the memory cellsconnected to the selected word line) for another embodiment of step 680of FIG. 13, in which the system will count the number of memory cellssupposed to be programmed to state C that have their threshold voltageless than VvcL. This waveform shows the programming pulse (Program)applied during step 672, the verify pulses (Verify) applied during step674 and the time period (count failed cells) for counting the failedcells during step 680 for parts of three iterations of the loopscomprising steps 672-686 of FIG. 13. Like FIG. 22, the waveform of FIG.23 pertains to a programming process that is only verifying for onestate. In the embodiment of FIG. 23, the verify operations (step 674)are performed between programming pulses. However, the counting of thefailed cells (count failed cells) of step 680 is performed during thenext program pulse. In this embodiment, like the embodiment of FIG. 21,step 680 (count failed cells) includes applying a voltage pulse of VvcLin order to test whether the memory cells have a threshold voltage of atleast VvcL. In one embodiment, the voltage pulse of VvcL is appliedprior to the next program pulse while the counting of failed cells isperformed concurrently with the next program pulse. Other methods oftesting the threshold voltage can also be used.

FIGS. 20-23 describe the use of a intermediate compare level (e.g.,VvcL) when performing step 680 for memory cells being programmed tostate C. In one set of embodiments, step 680 will be performed on memorycells being programmed to states other than state C (which is thehighest state, or most extreme state) by counting the number of memorycells that have not reached the respective verify compare levels (e.g.Vva and Vvb). Thus, programming to state A will stop when less than afirst predetermined number of memory cells intended to be programmed tostate A have not reached Vva, programming to state B will stop when lessthan a second predetermined number (may be the same or different thanthe first predetermined number) of memory cells intended to beprogrammed to state B have not reached Vvb, and programming to state Cwill stop when less than a first predetermined number of memory cellsintended to be programmed to state C have not reached VvcL.

In another set of embodiment, step 680 and 682 will only be performed bymemory cells being programmed to the highest, or most extreme, state(e.g. state C or state S7).

In another set of embodiments, step 680 will use a intermediate comparevalue for each state. For example, step 680 will use an intermediatecompare value for memory cells being programmed to state A that is lowerthan Vva and step 680 will use an intermediate compare value for memorycells being programmed to state B that is lower than Vvb.

In some embodiments, such as where the threshold voltages are loweredfor programming and raised during erase, the intermediate compare valuewill be higher than the verify compare value.

FIGS. 20-23 illustrate the use of an intermediate compare level (e.g.,VvcL) with memory cells that store two bits of data. However, theconcepts taught by FIGS. 20-23 can be applied to memory cells that storemore than two bits of data. For example, counting memory cells that havea threshold voltage less than the intermediate value in step 680 can beused with the programming processes of FIGS. 10 and 11. In one examplethat includes memory cells storing three bits of data, step 680 willcount memory cells that have threshold voltages less than the respectiveverify levels for S1-S6 (e.g., Vv1, Vv2, Vv3, Vv4, Vv5, Vv6) for memorycells being programmed to S1-S6 and count memory cells that are lessthan Vv7L for memory cells being programmed to state S7, where Vv7L is0.5v (or a different value) less than Vv7. In one alternative, Vv7L canbe equal to Vv6, Vv5 or another value near those values.

In another example that includes memory cells storing three bits ofdata, step 680 will count memory cells that have threshold voltages lessthan the respective verify levels for S1-S5 (e.g., Vv1, Vv2, Vv3, Vv4,and Vv5) for memory cells being programmed to S1-S5, count memory cellsthat are less than Vv6L for memory cells being programmed to state S6,and count memory cells that are less than Vv7L for memory cells beingprogrammed to state S7, where Vv6L is 0.5v (or a different value) lessthan Vv6.

FIG. 24 describes another embodiment where VvcL is set to be equal toVvb, or Vv7L is set to be Vv6. Additionally, after determining that thenumber of failed cells (e.g., cells having a threshold voltage that isless the intermediate compare value) is less than the predeterminednumber, a predetermined number of one or more additional programmingpulses is applied. In the embodiments that perform step 680 during thenext program pulse (see FIGS. 21 and 23), the predetermined number ofone or more additional programming pulses are applied after the nextprogram pulse. The process of FIG. 24 is similar to the process of FIG.13 (with like reference numbers depicting the same steps); however,steps 680 and 682 are replaced by steps 740-744. Step 740 is similar tostep 680 except that VvcL=Vvb or Vv7L=Vv6. Step 742 is similar to step682, except the predetermined limit compared to the failed cells may bedifferent. If the number of failed cells is greater than thepredetermined limit, than the process continues at step 684. If thenumber of failed cells is less than or equal to the predetermined limit,than the process continues at step 744. In step 744, a predeterminednumber of programming pulses are applied to the memory cells via theselected word line. Verify operations (with lockout for memory cellsthat verify successfully) are performed between these predeterminednumber of programming pulses. The predetermined limit and thepredetermined number of programming pulses can be determined based onsimulation or device characterization. In one embodiment, the limit andthe number of programming pulses are set dynamically based on number ofprogram-erase cycles, temperature or other factors, rather than bepredetermined.

FIG. 25 describes another embodiment that includes applying apredetermined number of programming pulses and concluding theprogramming after all memory cells intended to be programmed to state Bhave sufficiently been programmed to state B. It is assumed that whenafter all memory cells intended to be programmed to state B havesufficiently been programmed to state B, that a small number of memorycells intended to be programmed to state C do not yet have thresholdvoltages that have reached Vvb. The phrase “sufficiently programmed”means that enough memory cells have reached state B to consider theprogramming process successful. For example, when programming a group ofmemory cells to state B using the process of FIG. 13, the group ofmemory cells are sufficiently programmed when enough memory cells havesuccessfully verified such that the number of memory cells that havefailed verification is less than predetermined limit (e.g., thepredetermined limit that can be fixed with ECC). At this point, it isassumed that less than the predetermined limit of memory cells intendedto be programmed to state C would have failed verification for state Bif so tested. Therefore, only apply a predetermined additional set ofone or more programming pulses and then stop the programming. Whenapplying the additional set of one or more programming pulses (in thisembodiment or the embodiment of FIG. 24), there will be no countingfailed cells during or between the additional set of one or moreprogramming pulses. To achieve this embodiment, the memory cells beingprogrammed to state C will perform the process of FIG. 25, while thememory cells being programmed to states A and B will perform the processof FIG. 13.

The process of FIG. 25 is similar to the process of FIG. 13, with thefollowing exceptions. If, in step 676, it is determined that not allmemory cells have been properly verified, then in step 780 it isdetermined whether all memory cells intended to be programmed to state Bhave sufficiently been programmed to state B. If not, the processcontinues at step 684. If all memory cells intended to be programmed tostate B have sufficiently been programmed to state B, then in step 782 apredetermined number of programming pulses are applied to the memorycells via the selected word line. Verify operations (with lockout formemory cells that verify successfully) are performed between thesepredetermined number of programming pulses. The number of programmingpulses are applied to the memory cells during step 782 can be determinedbased on experimentation, simulation and/or device characterization. Theamount of the increment between programming pulses may affect the numberof programming pulses that are applied to the memory cells during step782.

The embodiment of FIG. 25 can also be used with memory cells storingmore than two bits of data. For example, the process of FIG. 25 can beused with memory cells being programmed as depicted in FIGS. 10 and 11H,as well as other programming processes. In one embodiment, when usingthe process of FIG. 25 with memory cells storing three bits of data,step 780 test whether all memory cells intended to be programmed tostate S6 (the second highest state) have sufficiently been programmed tostate S6.

One solution for achieving tight threshold voltage distributions,without unreasonably slowing down the programming process, includesusing a two-phase programming process. The first phase, a coarseprogramming phase, includes an attempt to raise a threshold voltage in afaster manner and paying less attention to achieving a tight thresholdvoltage distribution. The second phase, a fine programming phase,attempts to raise the threshold voltage in a slower manner in order toreach the target threshold voltage, while also achieving a tighterthreshold voltage distribution. One example of a coarse/fine programmingmethodology can be found in U.S. Pat. No. 6,643,188, incorporated hereinby reference in its entirety.

FIGS. 26A-C and 27A-C provide more detail of one example of acoarse/fine programming methodology. FIGS. 26A and 27A depict theprogramming pulses Vpgm applied to the control gate. FIGS. 26B and 27Bdepict the bit line voltages for the memory cells being programmed.FIGS. 26C and 27C depict the threshold voltage of the memory cells beingprogrammed. This example uses two verify levels, indicated in theFigures as Vver1 and Vver2. The final target level is Vver1. When athreshold voltage of the memory cell has reached Vver1, the memory cellwill be inhibited from further programming by applying an inhibitvoltage to the bit line corresponding to that memory cell. For example,the bit line voltage can be raised to Vinhibit (See FIG. 26B and FIG.27B). In one embodiment, Vinhibit is Vdd. However, when a memory cellhas reached a threshold voltage close to (but lower than) the targetvalue Vver1, the threshold voltage shift to the memory cell duringsubsequent programming pulses is slowed down by applying a certain biasvoltage to the bit line, typically in the order of 0.3v to 0.8v. Becausethe rate of threshold voltage shift is reduced during the next fewprogramming pulses, the final threshold voltage distribution can benarrower than otherwise. To implement this method, a second verify levelthat is lower than that of Vver1 is used. This second verify level isdepicted as Vver2. When the threshold voltage of the memory cell islarger than Vver2, but still lower than Vver1, the threshold voltageshift to the memory cell will be reduced for subsequent programmingpulses by applying a bit line bias Vs (FIG. 27B). Note that in thiscase, two verify operations are required for each state. One verifyoperation at the corresponding Vver1 for each state, and one verifyoperation at the corresponding Vver2 for each state. This may increasethe total time needed to program the memory cells. However, a largerΔVpgm step size can be used to speed up the process.

FIGS. 26A, 26B, and 26C show the behavior of a memory cell whosethreshold voltage moves past Vver2 and Vver1 in one programming pulse.For example, the threshold voltage is depicted in FIG. 26C to pass Vver2and Vver1 in between t2 and t3. Thus, prior to t3, the memory cell is inthe coarse phase. After t3, the memory cell is in the inhibit mode.

FIGS. 27A, 27B, and 27C depict a memory cell that enters both the coarseand fine programming phases. The threshold voltage of the memory cellcrosses Vver2 in between time t2 and time t3. Prior to t3, the memorycell is in the coarse phase. After t3, the bit line voltage is raised toVs; therefore, the memory cell is in the fine phase. In between t3 andt4, the threshold voltage of the memory cell crosses Vver1; therefore,the memory cell is inhibited from further programming by raising the bitline voltage to Vinhibit.

The technology described above with respect to stopping programming whenan estimated number of memory cells that have failed verification isless than a limit can be used with the coarse/fine programming describedwith respect to FIGS. 26A-C and 27A-C (or a different type ofcoarse/fine programming). The intermediate value used to estimate thenumber of memory cells that have failed verification can be Vver2.

One embodiment includes applying a programming signal to a first set ofnon-volatile storage elements in order to program the first set ofnon-volatile storage elements to a first target condition, determiningwhether the amount of non-volatile storage elements of the first setthat have not yet reached an intermediate condition is less than acompare value, and concluding programming of the first set ofnon-volatile storage elements in response to determining that the amountof non-volatile storage elements of the first set that have not yetreached the intermediate condition is less than the compare value. Theintermediate condition is different than the first target condition.

One embodiment includes a first set of non-volatile storage elements andone or more managing circuits in communication with the first set ofnon-volatile storage elements. The one or more managing circuits performa programming process on the first set of non-volatile storage elementsto program the first set of non-volatile storage elements to a firsttarget condition. The programming process includes the one or moremanaging circuits applying a programming signal to the first set ofnon-volatile storage elements and verifying whether the first set ofnon-volatile storage elements have reached the first target condition.The one or more managing circuits determine a number of non-volatilestorage elements of the first set that have not yet reached anintermediate condition during the programming process. The intermediatecondition is different than the first target condition. The one or moremanaging circuits conclude the programming process for the first set ofnon-volatile storage elements if the number of non-volatile storageelements of the first set that have not yet reached the intermediatecondition is less than the compare value.

One embodiment includes applying a programming signal to a plurality ofnon-volatile storage elements in order to concurrently program thenon-volatile storage elements to different target conditions, verifyingwhether the non-volatile storage elements have reached their respectivetarget conditions, counting non-volatile storage elements of the firstsubset that have not yet reached an intermediate condition with respectto the highest target condition, and concluding programming of thenon-volatile storage elements in response to counting less than apredetermined number of the non-volatile storage elements of the firstsubset to have not yet reached the intermediate condition anddetermining that other non-volatile storage elements intended for othertarget conditions of the different target conditions are sufficientlyprogrammed. Non-volatile storage elements reaching the highest targetcondition pass through the intermediate condition. The different targetconditions include a lowest target condition and a highest targetcondition. The programming signal includes a set of pulses. Theplurality of non-volatile storage elements includes a first subset ofnon-volatile storage elements being programmed to the highest targetcondition. The verifying includes performing one or more verifyingprocesses between pulses.

One embodiment includes applying a programming signal to a plurality ofnon-volatile storage elements in order to program the non-volatilestorage elements to different target conditions. The programming signalincludes a set of pulses. The different target conditions include afirst target condition and a second target condition. The plurality ofnon-volatile storage elements includes a first subset of non-volatilestorage elements being programmed to the first target condition and asecond subset of non-volatile storage elements being programmed to thesecond target condition. The method further comprises verifying whetherthe second subset of non-volatile storage elements have sufficientlyreached the second target condition, applying a predetermined number ofone or more pulses to the first subset of non-volatile storage elementsin response to determining that the second subset of non-volatilestorage elements have sufficiently reached the second target condition,and concluding programming of the first subset of non-volatile storageelements in response to and after applying the predetermined number ofone or more pulses to the first subset of non-volatile storage elements.

The foregoing detailed description of the invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching. The described embodiments were chosen in order to best explainthe principles of the invention and its practical application, tothereby enable others skilled in the art to best utilize the inventionin various embodiments and with various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto.

1. A method of programming non-volatile storage, comprising: applying aprogramming signal to a first set of non-volatile storage elements inorder to program the first set of non-volatile storage elements to afirst target condition; determining whether the amount of non-volatilestorage elements of the first set that have not yet reached anintermediate condition is less than a compare value, the intermediatecondition is different than the first target condition; and concludingprogramming of the first set of non-volatile storage elements inresponse to determining that the amount of non-volatile storage elementsof the first set that have not yet reached the intermediate condition isless than the compare value.
 2. The method of claim 1, furthercomprising: verifying whether the first set of non-volatile storageelements have reached the first target condition.
 3. The method of claim2, wherein: the programming signal includes a set of pulses; theverifying includes performing one or more verifying processes betweenpulses; and the determining includes counting non-volatile storageelements of the first set that have not yet reached the intermediatecondition during at least some of the pulses.
 4. The method of claim 2,wherein: the programming signal includes a set of pulses; the verifyingincludes performing one or more verifying processes between pulses; andthe determining includes counting non-volatile storage elements of thefirst set that have not yet reached the intermediate condition betweenpulses.
 5. The method of claim 1, wherein: the first target condition isa threshold voltage range; and the intermediate condition is a thresholdvoltage level that is a lower voltage level than the first targetcondition.
 6. The method of claim 1, wherein the determining whether theamount of non-volatile storage elements of the first set that have notyet reached an intermediate condition is less than a compare valuecomprises: counting non-volatile storage elements of the first set thathave not yet reached the intermediate condition; and comparing thenumber of non-volatile storage elements counted to a predeterminedvalue.
 7. The method of claim 1, wherein: the amount of non-volatilestorage elements of the first set that have not yet reached theintermediate condition is proportional to how many non-volatile storageelements of the first set have not yet reached the target condition. 8.The method of claim 1, wherein: the applying of a program signal is partof a programming process that programs a plurality of non-volatilestorage elements to different target conditions, the different targetconditions include a lowest target condition and a highest targetcondition, the plurality of non-volatile storage elements include thefirst set of non-volatile storage elements, the first target conditionis the highest target condition.
 9. The method of claim 1, wherein: theapplying of a program signal concurrently programs a plurality ofnon-volatile storage elements to different target conditions, thedifferent target conditions include a lowest target condition and ahighest target condition, the plurality of non-volatile storage elementsinclude the first set of non-volatile storage elements, the first targetcondition is the highest target condition; and the process furtherincludes verifying whether the first set of non-volatile storageelements have reached the first target condition.
 10. The method ofclaim 1, wherein: the process further includes verifying whether thefirst set of non-volatile storage elements have reached the first targetcondition, the verifying includes performing one or more verifyingprocesses between at least a subset of the pulses; the programmingsignal includes a set of pulses; the first target condition is athreshold voltage range; the intermediate condition is a thresholdvoltage level that is a lower voltage level than the first targetcondition; and the determining whether the amount of non-volatilestorage elements of the first set that have not yet reached anintermediate condition is less than a compare value comprises countingnon-volatile storage elements of the first set that have not yet reachedthe intermediate condition and comparing the number of non-volatilestorage elements counted to a predetermined value.
 11. The method ofclaim 1, wherein: the first set of non-volatile storage elements areassociated with a set of data states, the first target condition is oneof the set of data states, the intermediate condition is a verify valuefor a different data state of the set of data states.
 12. The method ofclaim 1, wherein: the programming signal includes a set of pulses; thefirst set of non-volatile storage elements are associated with a set ofdata states, the first target condition is one of the set of datastates, the intermediate condition is a verify value for a differentdata state of the set of data states; the method further includesapplying a predetermined number of one or more pulses to the first setof non-volatile storage elements in response to determining that theamount of non-volatile storage elements of the first set that have notyet reached the intermediate condition is less than the compare value;and the programming of the first set of non-volatile storage elements isconcluded after the applying the predetermined number of one or morepulses to the first set of non-volatile storage elements.
 13. The methodof claim 1, wherein: the first set of non-volatile storage elements aremulti-state flash memory devices.
 14. A method of programmingnon-volatile storage, comprising: applying a programming signal to aplurality of non-volatile storage elements in order to concurrentlyprogram the non-volatile storage elements to different targetconditions, the different target conditions include a lowest targetcondition and a highest target condition, the programming signalincludes a set of pulses, the plurality of non-volatile storage elementsincludes a first subset of non-volatile storage elements beingprogrammed to the highest target condition; verifying whether thenon-volatile storage elements have reached their respective targetconditions, the verifying includes performing one or more verifyingprocesses between pulses; counting non-volatile storage elements of thefirst subset that have not yet reached an intermediate condition withrespect to the highest target condition, non-volatile storage elementsreaching the highest target condition pass through the intermediatecondition; and concluding programming of the non-volatile storageelements in response to counting less than a predetermined number of thenon-volatile storage elements of the first subset to have not yetreached the intermediate condition and determining that othernon-volatile storage elements intended for other target conditions ofthe different target conditions are sufficiently programmed.
 15. Themethod of claim 14, wherein: the counting is performed during pulses.16. The method of claim 14, wherein: the counting is performed betweenpulses.
 17. The method of claim 14, further comprising: applying apredetermined number of one or more pulses to the first subset ofnon-volatile storage elements in response to counting less than thepredetermined number of the non-volatile storage elements of the firstsubset to have not yet reached the intermediate condition, theconcluding programming is performed after the applying the predeterminednumber of one or more pulses.
 18. The method of claim 14, wherein: thefirst set of non-volatile storage elements are multi-state flash memorydevices.
 19. A method of programming non-volatile storage, comprising:applying a programming signal to a plurality of non-volatile storageelements in order to program the non-volatile storage elements todifferent target conditions, the programming signal includes a set ofpulses, the different target conditions include a first target conditionand a second target condition, the plurality of non-volatile storageelements includes a first subset of non-volatile storage elements beingprogrammed to the first target condition and a second subset ofnon-volatile storage elements being programmed to the second targetcondition; verifying whether the second subset of non-volatile storageelements have sufficiently reached the second target condition; applyinga predetermined number of one or more pulses to the first subset ofnon-volatile storage elements in response to determining that the secondsubset of non-volatile storage elements have sufficiently reached thesecond target condition; and concluding programming of the first subsetof non-volatile storage elements in response to and after applying thepredetermined number of one or more pulses to the first subset ofnon-volatile storage elements.
 20. The method of claim 19, wherein: thefirst subset of non-volatile storage elements and the second subset ofnon-volatile storage elements are multi-state flash memory devicesconnected to a common word line.
 21. The method of claim 19, wherein:the verifying is performed multiple times, each time between a pair ofconsecutive pulses; and the different target conditions are thresholdvoltage ranges.
 22. The method of claim 19, wherein: the applying theprogramming signal to the plurality of non-volatile storage elementsconcurrently programs the first subset of non-volatile storage elementsand the second subset of non-volatile storage elements.
 23. The methodof claim 19, wherein: the first target condition is a higher thresholdvoltage range; and the second target condition is a lower thresholdvoltage range.